Lifetime Measurements of Excited States in Pt172 and the Variation of Quadrupole Transition Strength with Angular Momentum

B. Cederwall et al.
Phys. Rev. Lett. 121, 022502 – Published 10 July 2018

Abstract

Lifetimes of the first excited 2+ and 4+ states in the extremely neutron-deficient nuclide Pt172 have been measured for the first time using the recoil-distance Doppler shift and recoil-decay tagging techniques. An unusually low value of the ratio B(E2:41+21+)/B(E2:21+0gs+)=0.55(19) was found, similar to a handful of other such anomalous cases observed in the entire Segré chart. The observation adds to a cluster of a few extremely neutron-deficient nuclides of the heavy transition metals with neutron numbers N9094 featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low B(E2:41+21+)/B(E2:21+0gs+) ratios observed in these cases. Such low values cannot, e.g., be explained within the framework of the geometrical collective model or by algebraic approaches within the interacting boson model framework. It is proposed that the group of B(E2:41+21+)/B(E2:21+0gs+) ratios in the extremely neutron-deficient even-even W, Os, and Pt nuclei around neutron numbers N9094 reveal a quantum phase transition from a seniority-conserving structure to a collective regime as a function of neutron number. Although a system governed by seniority symmetry is the only theoretical framework for which such an effect may naturally occur, the phenomenon is highly unexpected for these nuclei that are not situated near closed shells.

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  • Received 23 March 2018
  • Revised 19 April 2018
  • Corrected 9 August 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.022502

© 2018 American Physical Society

Physics Subject Headings (PhySH)

Nuclear Physics

Corrections

9 August 2018

Correction: The name of the ninth author had been missing in the original publication and has been inserted.

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Issue

Vol. 121, Iss. 2 — 13 July 2018

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